Old city the one above all others? Not quite (6)
I believe the answer is:
thebes
'old city' is the definition.
(ancient Greek city)
'the one above all others? not quite' is the wordplay.
'the one above all others?' becomes 'the best'.
'not quite' means to remove the last letter.
'thebest' with its final letter taken away is 'THEBES'.
(Other definitions for thebes that I've seen before include "Greek city of Oedipus" , "Old Egyptian city" , "Ancient city of upper Egypt" , "place in Greece" , "One of the oldest Greek cities" .)